The invention relates to a coiled-heat-exchanger-type water heater, and more specifically to a corrosion-resistant coating for the heat exchanger coil of that type of water heater. The anti-corrosive coatings and coating methods described herein are also applicable to linear-heat-exchanger-type water heaters.
In known coiled-heat-exchanger-type water heaters, such as a Legend Burkay(copyright) Boiler manufactured by A. O. Smith Corporation headquartered in Milwaukee, Wis., water flows through the heat exchanger while hot products of combustion flow over the outside of the heat exchanger. If the water in the heat exchanger is too cold, some of the gases in the products of combustion may reach their dew points and condense on the heat exchanger. As a result, a condensation of corrosive-combustion products may form on the heat exchanger, thereby leading to corrosion of the coil. This, in turn, may cause inefficiencies in, or even failure of (i.e., leaking), the heat exchanger. More particularly, the corrosion products can accumulate on and between heat-transfer or finned surfaces extending from the heat exchanger, thereby resulting in restricted airflow through the heat exchanger. The restricted airflow can cause problems with combustion and also cause eventual leakage of the heat exchanger.
One known way to prevent corrosion in the heat exchanger is to coat the heat exchanger with lead. The typical process for this measure includes dipping the heat exchanger into a molten pool of lead to obtain complete coating of the heat exchanger. This process is typically no longer used due to the hazards associated with lead.
Another known way to combat such corrosion is to raise the temperature of the water being introduced into the heat exchanger to reduce the likelihood of condensation. This is sometimes done by routing or recirculating some of the hot water from the exit of the heat exchanger back to the inlet to mix with the cold water being introduced, thereby raising the temperature of the coil above the dew point. Such recirculation systems often require a pump and control system which can add cost and complexity to the system.
The invention provides a copper-finned heat exchanger for a water heater. The heat exchanger comprises a conduit through which water runs, heat-transfer fins extending from the conduit and an anti-corrosive coating comprising electroless nickel. The heat-transfer fins are made preferably of copper, and the coating is deposited directly onto at least one of the copper heat-transfer fins. In one embodiment of the invention, the anti-corrosive coating is about 0.05 mils to about 10 mils in thickness.
In addition, the invention provides a water heater. The water heater comprises a housing, a combustor positioned within the housing, a flue positioned above the combustor in the housing and a copper-coiled heat exchanger positioned within the housing. The heat exchanger has a conduit through which water runs, and heat-transfer fins extend therefrom. An anti-corrosive coating is chemically deposited directly onto a portion of the copper heat exchanger, and the anti-corrosive coating preferably includes electroless nickel. The anti-corrosive coating may be about 0.05 mils to about 10 mils in thickness.
Furthermore, the invention provides a method of preventing corrosion of a heat exchanger for a water heater. The method comprises immersing a copper heat exchanger into an aqueous-chemical-deposition bath comprising at least one of nickel, cobalt, palladium or platinum. The method further comprises electroless-chemically depositing an electroless coating selected from the group consisting of nickel, cobalt, palladium, platinum or a combination thereof onto at least a portion of the heat exchanger. The electroless coating prevents corrosion of the heat exchanger when the heat exchanger is used in conjunction with a functioning water heater.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.